1. Field of the Invention
This invention relates to a release sheet and more particularly, a release sheet which is used in making synthetic leather, and a method for making the release sheet.
2. Description of the Prior Art
Synthetic leather has usually been manufactured by using what is called "a release sheet". The release sheet comprises a backing sheet and a release resin layer. On the surface of the release resin layer or a peeling surface thereof, there is often embossed an uneven pattern which is complementary to wrinkles and pores of the skin and the like inherent in natural leather. The surface of the release resin layer or the peeling surface is coated with synthetic leather material such as polyurethane resin and then, backing cloth is laminated on the synthetic leather material coating, after which the release sheet is peeled to give synthetic leather. The synthetic leather thus formed comprises the backing cloth and the synthetic leather material. On the surface of the synthetic leather, an irregular pattern similar to the surface pattern inherent in natural leather is formed.
Before being fabricated, natural leather is usually dyed. It is unevenly dyed to form an irregularly dyed pattern or what is called "a cloudy pattern". It is, therefore desired to give the cloudy pattern to the surface of synthetic leather so that the appearance of natural leather is given on synthetic leather thus formed. Several techniques are known in the art to provide synthetic leather with the cloudy pattern.
Generally, no cloudy pattern is formed by simply dyeing synthetic leather. Thus, a printing method is known wherein a gravure coater provided with an engraved roll is used to print the cloudy pattern on the synthetic leather surface. This method has a disadvantage that the irregular pattern corresponding to wrinkles and pores formed on the synthetic leather surface is covered by the printing ink. Another method is also known wherein a knife coater provided with a back-up roll having an engraved cloudy pattern is used to form the pattern on the synthetic leather surface. But, this method has also the same disadvantage as the gravure coater method, neither of the two methods is economical because numbers of rolls are necessary for the cloudy pattern required. Furthermore, the two methods have poor reproducibility and need a certain extent of skill to perform them.